It is standard for a photographic negative strip to carry at the center of each exposure at one edge of the strip a notch, and at the opposite edge in a corresponding location the number of the individual negative or exposure. These exposure numbers make it easy to identify a single exposure on a negative strip for printing.
Unfortunately, however, the problem remains of determining which proof is associated with which numbered negative exposure. Even though the prints of a negative strip are normally made on a paper strip that carries on one edge notches that lie between successive prints, there is nothing to identify which in a succession any single proof is since the proofs are normally cut off the print strip. This is largely due to the fact that the negative strip is in fact the strip exposed by the photographer and is normally supplied and developed in specific lengths, while the print paper strip used for the prints from that negative strip is actually nothing more than a section of a long supply strip held on a roll in the print-making machine. In fact for a photographer who may dispose of a handful of nearly identical photographs, it can be virtually impossible to determine without making a print which negative a given photograph came from.